Storing and transporting hazardous fluids in vessels can be a dangerous business. Hazardous fluids are often extremely corrosive causing vessel interiors to deteriorate very rapidly. To slow the deterioration, many vessel interiors are coated with a non-corrosive lining, such as Teflon, Rubber, Fiberglass Reinforced Plastic, and others. Even with the use of non-corrosive linings, all vessels eventually wear and deteriorate ultimately producing cracks that can leak hazardous fluid into the environment. In addition to harming the environment, these leaks can be violations of the law. In an effort to protect the environment and follow the law, an entire industry has developed creative technology to detect and prevent leaks in these vessels. While some of this technology has been successful in detecting leaks, it has also proven to be expensive, labor-intensive, and sometimes unreliable.
One popular method for detecting leaks in a vessel is Holiday spark testing. This method comes in two varieties, low-voltage and high-voltage. Using the low voltage method, a ground wire and a lead wire are connected to a low-voltage battery. The ground wire is connected to the outside of a vessel and the lead wire is connected to a wet sponge. In operation, the wet sponge is moved over the non-corrosive lining. If there is a crack in the lining, the circuit is completed activating an audible or visual indicator.
While this device is inexpensive and relatively easy to use, it has drawbacks. First, the vessel in service must be completely empty of fluid and dry before spark testing can begin due to safety and operational concerns. This has a number of consequences. If not completely dry, any remaining fluid in the vessel can cause a short and falsely indicate a crack or the wrong location. Even worse, if the vessel contained flammable fluids there is the risk of igniting the remaining fluid. Another consequence of removing the fluid from the tank is that some cracks may become undetectable with the fluid removed.
When a vessel is filled with fluid, the pressure exerted on the vessel by the specific gravity and temperature of the fluid can enlarge cracks that otherwise shrink and disappear when the fluid is removed and the pressure is relieved. A second drawback of low-voltage testing is that spark testing is not sensitive enough to indicate inadequate thickness in the tank lining, which leads to premature failure of the lining. Third, locating a crack in the lining with this device is very time consuming. To operate a spark tester, an operator must manually sweep the spark tester over the entire lining of the tank. Not only is this process time consuming, but it also requires a degree of skill and experience from the operator. Finally, this method is not capable of early detection of weakness in the lining, such as thinning. It only detects weaknesses that have developed into full-fledged cracks. As a result, spark testing must be routinely performed to detect cracks quickly after they develop to prevent leaking. All of these disadvantages result in high maintenance and repair costs along with loss of production time.
High-voltage spark testing is very similar to low-voltage spark testing, except an electrode is used instead of a wet sponge and a high-voltage power source is used instead of a low-voltage battery. When a crack in the lining is detected, an electrical arc is visible between the electrode and the lining. The electrical arc acts as a visual indicator of a crack in the lining. The high-voltage power source allows this method to indicate inadequate thickness in the tank lining. Like low-voltage spark testing, the tank must be empty of fluid and dry. This method has all the same drawbacks as low-voltage spark testing. In fact, there is an increased risk of igniting residual flammable fluids. Additionally, repeated high-voltage spark testing leads to breakdown of the lining. Again, these disadvantages result in high maintenance and repair costs along with loss of production time.
Other methods for detecting leaks allow for continuous testing while the vessel is still filled with fluid. One such method is specifically described in U.S. Pat. No. 5,214,387, hereafter referred to as '387. Multiple probes are embedded in a vessel wall at various depths. A separate probe is submerged in the fluid within the vessel. An electrical monitor connected to all the probes communicates an electrical signal through the submerged probe into the fluid. If a crack in the vessel lining develops, fluid will penetrate the crack and contact the probes in the vessel wall, thus, completing an electrical circuit. The electrical monitor registers this signal and activates an audible or visible indicator.
However, there are numerous problems with this method of leak detection. First, the ability to detect leaks is dependent on the number and placement of the probes. Therefore, leaks that develop in an area not monitored by a probe may never be detected. To address this concern, '387, discloses a mat built within the entire structure of the vessel. However, this only results in another problem. A mat will detect a leak anywhere in the vessel, but will not indicate exactly where the leak is located. Consequently, Holiday spark testing must be subsequently performed to identify the actual location of the leak. A second problem with this method is contamination and corrosion of the probes. When this happens, the probes become ineffective preventing detection of leaks. These problems can result in the non-detection or late detection of a leak resulting in increased expenses for maintenance and repair.
Another method for continuous testing while the vessel is still filled with fluid is specifically described in U.S. Pat. No. 5,378,991, hereafter referred to as '991. In this method, the vessel has an inner conductive layer. It also has a probe that is submerged in the fluid. An electrical monitor connected to the inner conductive layer communicates an electrical signal through the submerged probe into the fluid. If a crack in the vessel lining develops, fluid will penetrate the crack and contact the inner conductive layer, thus, completing an electrical circuit. The electrical monitor registers this signal and activates an audible or visible indicator.
However, the problems with this method of leak detection are similar to the method in '387. First, the inner conductive layer will detect any leak present in the vessel, but will not indicate exactly where the leak is located. Consequently, Holiday spark testing must be subsequently performed to identify the actual location of the leak. A second problem with this method is contamination and corrosion of the probe. When this happens, the probe becomes ineffective preventing detection of leaks. These problems can result in the non-detection or late detection of a leak resulting in increased expenses for maintenance and repair.
Fortunately, the present invention overcomes the problems associated with methods described above. Using the present invention, both leaks and premature wearing can be detected while a vessel is filled with fluid, preventing high maintenance costs along with lost production time. In addition, the present invention specifically pinpoints the location of leaks in a vessel.